North Korea warns the South of attack, following anti-Pyongyang protests

North Korea has warned it could strike the South without warning, after activists burned effigies of the ruling Kim dynasty earlier this week.

South Korea's defence ministry says the threat was made in a message sent by the North's highest military body through a hotline.

South Korean activists burned effigies of North Korean leader Kim Jong-Un and his late father and grandfather in anti-Pyongyang protests on Tuesday.

The rallies coincided with commemorations in North Korea, which were marking the second anniversary of the death of Kim Jong-Il.

The North said the rallies had insulted the "highest dignity" of its leadership and threatened to take "merciless" retaliatory acts without prior warning, Seoul's defence ministry said.

"We've sent a reply vowing to react sternly to any provocations by North Korea," ministry spokesman Kim Min-Seok said.President Park to hold weekly security talks

Meanwhile, South Korea has announced it will set up a new security control tower to counter threats from Pyongyang, while a standing committee and secretariat of the National Security Council would be established.

Ju Chul-Ki, a top security official in the office of President Park Geun-Hye, said that will see the president hold high-level security talks about once a week.

Such security talks are currently only held on orders from President Park.

Seoul remains on alert, after the man who had previously been North Korea's second most powerful man was executed.

Jang Song-Thaek was the uncle and previous mentor of leader Kim Jong-Un.

Both South Korea and the United States have warned of possible provocative acts by the nuclear-armed North.